Essential elements of every transponder unit are the wire coil attached on a substrate, such as a chip card, and the electronic circuit which, is also attached on the chip card. The latter is called a chip. For the most part, in modern manufacturing methods the wire coil is not first wound as an air-core coil and then baked together with the substrate, but that the wire is directly laid onto the substrate to form a wire coil, for example, by being embedded into the plastic of the substrate by ultrasonic welding. The German Published Patent Application 44 10 732 A1 describes the details of such a wire laying method.
In the manufacture of such a transponder unit, bonding the ends of the coils with the terminal areas of the chip still creates a special problem. This is due, in particular, to the very small dimensions of the components that are to be connected with each other. A chip unit's terminal areas, which mostly or substantially are formed to have a square shape, as a rule have a relatively small side length. Particularly in the low-frequency range, a copper wire, the diameter of which for the most part is in the range of 50 μm, is usually used as the coil wire. In view of these dimensions it becomes clear that some care must be taken so as to really align the wire sufficiently with the terminal areas of the chip when connecting them.
It has already been proposed that one and the same tool be used for laying the wire onto the substrate and for bonding the wire with the chip, compare DE 43 25 334 A1. If there is an intention of using one and the same tool both for laying the wire onto the substrate and connecting the wire to the terminal areas of the chip unit in one process step, attention must not only be paid to the tact that the wire must be guided very precisely at said tool in order to ensure that the same position of the wire is very precisely allocated to one certain position of the tool. There is, rather, the additional problem that the means for connecting the wire with the substrate and the additional means for connecting or welding the wire must be integrated into the tool in a very small space indeed. This is necessary so that the position at which the wire is to be laid onto the substrate or connected with the chip can be set by the controlling device or controller with sufficient precision both during laying as well as during connecting. This integration entails a considerable effort with regard to the tools and, furthermore, does not allow for an optimal operating speed. Because in such an integration it is not possible to carry out the laying of the wire onto the substrate and the bonding of wire with the terminal areas of the chip independently from one another, i.e., it is not possible to proceed with laying the wire whilst the wire is connected with the first terminal area of the chip.
A totally different approach is proposed by EP 0 880 754 B1. In order to reduce the number of working steps, this printed publication teaches not to pre-mount the chip or “chip unit” onto a bonding substrate with enlarged terminal areas, but to bond them directly. For this purpose, this approach provides a first step within whose context the wire is first guided over the terminal area on the chip unit and fixed on the substrate relative to the terminal area of the chip unit. An exactly defined orientation of the wire relative to the terminal area on the chip unit is achieved with this first step. It is not until then that the connection of the wire with the terminal area is carried out in a second step.
In practical application, these two steps are carried out in the following manner: the wire laying device connects the wire with the substrate, then draws the wire over the first terminal area of the chip unit in order to then connect the wire with the substrate behind the terminal area of the chip unit again, thus to lay the coil on the substrate. Once the coil has been laid completely and the wire laying device has arrived at the second terminal area of the chip unit, it draws the chip over the second terminal area and, behind the second terminal area, connects it with the substrate again for a certain distance.
This solution works actually works rather well in practical use. It allows for the laying of the wire onto the substrate and the connecting of the wire with the terminal areas located immediately on the chip unit to be carried out in two different, spatially separate work stations—the substrate with the finished wound coil and the wire drawn over the terminal areas of the chip unit can be taken from the first working station and transferred to a second working station. There, the wire strung over the terminal areas is approached by a tool and connected by it with the terminal areas. However, problems particularly occur in the case where the chip unit that is only loosely inserted in the window of the card unit is displaced relative to the card substrate for whatever reason during the further transport.
In this context, the following should be known: It is often expedient for the card substrate and the chip module to run through various processing stations of a manufacturing machine before they finally become the finished RFID card. For example, the window is punched into the card substrate in a first processing station. The card substrate thus processed is then conveyed on to a second processing station. In this station, the chip module is inserted into said window, without being connected with the card substrate, of course. This ensemble of card substrate and the chip module is conveyed on to a third processing station. At this station, the wire is laid on the substrate. Finally, the ensemble is conveyed into a fourth processing station in which the wire is connected in an electrically conductive manner with the bonding areas of the chip or of the chip module provided for this purpose. It is only in a subsequent processing station, which in most cases is the fifth, that the card substrate and the chip or chip module are firmly connected with each other by laminating them with suitable cover layers.
As long as the card substrate and the chip or chip module are not even connected by means of the wire terminal, considerable displacements in the position of the chip or chip module relative to the card substrate may occur, because each of the above-mentioned transport processes from one processing station to another can lead to a displacement in position. Displacements in position may also be caused by the card substrate heating up more than only to an inconsiderable extent during the laying of the wire, for heat energy is applied to the card substrate in a considerable extent in particular during the laying of the wire by means of ultrasonic friction welding.
As stated above, these almost unpredictable shifts in position may cause problems if the goal is to hit the terminal areas of the chip or the chip unit, too, with the wire in order to establish an electrically conductive connection.
As a consequence, the wire then is not drawn over the terminal area concerned of the chip or chip module at all, or only with an insufficient degree of covering. Thus, a faulty bonding between the wire and the terminal area of the chip or chip module may possibly occur in the second station.
In view of all this, it is the object of the invention to provide a laying method, wherein the laying of the wire onto the substrate can proceed independently from the connection of the wire with the chip module and which allows the compensation particularly of such tolerances as may occur by unintended relative movement between the card substrate and the chip module.